Many devices used in biomedical applications require that the bulk of the device have one property, while the surface of the device has another property. For example, contact lenses may have high oxygen permeability through the lens to maintain good corneal health. However, materials that exhibit exceptionally high oxygen permeability (e.g. polysiloxanes) are typically hydrophobic and will adhere to the eye. Thus, a contact lens generally has a core or bulk material that is highly oxygen permeable and hydrophobic, and a surface that has been treated or coated to increase hydrophilic properties, thereby allowing the lens to freely move on the eye without binding excessive amounts of tear lipid and protein.
In order to modify the hydrophilic nature of a relatively hydrophobic contact lens material, a coating may be applied onto the surface of a contact lens using a number of technologies, including a plasma treatment process, a Langmuir-Blodgett deposition process, a controlled spin casting process, a chemisorption process, a vapor deposition or a layer-by-layer polymer adsorption process.
The layer-by-layer polymer adsorption (LbL) process could be one useful process for increasing hydrophilic properties of contact lenses. By dipping iteratively one or more lenses in an alternating fashion to a polyanion (e.g., polyacrylic acid, PAA) solution and then a polycation (polyallylamine hydrochloride, PAH) solution, a LbL coating can be formed on the surfaces of lenses. A LbL coating on an ophthalmic lens can increase hydrophilic properties and thereby allow the lens to freely move on the eye without binding excessive amounts of tear lipid and protein. The on-eye movement is one of important criteria for wearing comfort.
Generally, LbL coating of lenses is carried out with the help of lens-carrying cages which each comprise a male and female basket halves. Many such cages can be affixed together to form trays of baskets. Such trays may then be placed side-by-side to allow hundreds or thousands of lenses to be simultaneously processed with a coating solution. Such trays may also be used in other manufacturing processes of ophthalmic lenses, such as washing, extracting, coating, drying and the like.
Currently, various types of fixtures and baskets are used for holding lenses in those manufacturing processes. Generally, such baskets are made of a plastic but it can be made of any fabricated material. The structure of a basket can be a pair of half-spheres, which have curved surfaces to fit the curvature of an ophthalmic lens. The curved surface is not a solid blank piece. It is partially cut open so that a fluid such as washing solution, water, or extraction media, can freely pass through the basket while an ophthalmic lens is held in place. Currently available baskets with a lattice network structure generally have a percentage of opening surface over total surface being in the range of 25%-50%. This would give a sufficient fluid flow while holding ophthalmic lens in place during a process.
However, those currently available baskets still have a relatively high percentage of solid surface available for a lens to contact. It is known that ophthalmic lenses may tend to stick to the solid surface of baskets under contact because of hydrophobic-hydrophobic interactions and/or bindings between surface oligomers. A high percentage of solid surface will be susceptible to the adhesion of a lens to a basket and prevent the lens from being treated uniformly during a washing, extracting, coating, or drying process. This could affect the efficiency of a process for treating lenses and therefore could be a problem for the production. Therefore, there is a need for a basket with a design that could minimize and/or eliminate the adhesion of a lens onto a basket.
Furthermore, when a lens-holding basket or tray is used in a LbL coating process, some chemicals such as polyelectrolytes tend to adhere onto the surface of the basket or tray to form an unwanted coating. Such coating on the basket or becomes thicker and brittle as the basket is repeatedly used in LbL coating process. It is very likely that this unwanted coating will flake or fracture off from the basket surface during a LbL coating process. If flakes of the unwanted coating adhere onto a lens to be coated, they can mask some portions of a lens and preventing those portions of lenses from being coated, producing lenses with coating defects. To eliminate this undesirable phenomenon occurring, the unwanted LbL coating needs to be abraded using a physical means. Such physical removal process of the unwanted LbL coatings from baskets is long, tedious and labor intensive and may damage the surfaces of the baskets. Therefore, there is a need for a method of efficiently removing any unwanted coatings on baskets.
An object of the invention is to eliminate such problems by providing an essential “contactless” surface of baskets to ophthalmic lenses.
Another object of the invention is to provide a method for cleaning efficiently baskets or trays containing baskets to remove any unwanted coatings from the surfaces of the baskets or trays without damaging their surfaces.